The production of benzotriazole is disclosed in U.S. Pat. Nos. 2,861,078 to Miller et al, 3,227,726 to Levy and in 3,564,001 to Long. The Miller et al patent also discloses the production of various substituted triazoles, including both of the tolyltriazole isomers, and the purification of triazoles by carbon treatment. Both Levy and Long disclose the purification of triazoles by vacuum distillation.
It has also been suggested that benzotriazole of a lower degree of purity than is ultimately desired in antifreeze can be dissolved in ethylene glycol and co-distilled therewith, presumably effecting a purification of both the benzotriazole and the ethylene glycol.